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479Vol. 52, N°3, 2017Revista de Biología Marina y Oceanografía

Revista de Biología Marina y OceanografíaVol. 52, N°3: 479-494, diciembre 2017DOI 10.4067/S0718-19572017000300006

ARTICLE

Oceanographic conditions and marine mammals:identifying a potential relationship in the coastal

region of the Mexican Central PacificCondiciones oceanográficas y mamíferos marinos: identificando una posible

relación en la región costera del Pacífico Central Mexicano

Tadashi Kono-Martínez1, Christian D. Ortega-Ortiz1*, Aramis Olivos-Ortiz2,Ernesto Torres-Orozco1 and Eduardo González-Rodríguez3

1Facultad de Ciencias Marinas, Universidad de Colima, Km 20 Carr. Manzanillo-Barra de Navidad, C.P. 28860, Manzanillo, Col., México.*Corresponding author: [email protected] Universitario de Investigaciones Oceanológicas, Universidad de Colima, Km 20 Carr. Manzanillo-Barra de Navidad, C.P. 28860,Manzanillo, Col., México3Centro de Investigación Científica y de Educación Superior de Ensenada, Unidad La Paz, Miraflores No. 334 e/ Mulegé y La Paz, C.P.23050, La Paz, B.C.S., México

Resumen.- Se investigaron las condiciones oceanográficas que podrían influir en la riqueza y distribución de mamíferos marinosen costas del Pacífico Central Mexicano durante el 2011. Las observaciones de mamíferos marinos se realizaron desde dosplataformas de investigación. Se muestrearon mensualmente 6 estaciones, donde se realizaron lances de CTD hasta 100 m y setomaron muestras de agua para determinación de nutrientes inorgánicos; y otras 15 estaciones fueron muestreadas solamentedurante invierno en una región más amplia. Se utilizaron imágenes de satélite (MODIS-AQUA L2) para obtener valores de temperaturasuperficial del mar (TSM) y clorofila (Chl-a); y datos de altimetría para identificar estructuras dinámicas de mesoescala en laregión. Durante invierno-primavera se encontraron valores altos de salinidad (34,6), valores bajos de nitratos y nitritos (~3-4µM), silicatos (5-7 µM) y clorofila (~10 mg m-3); como también valores bajos de temperatura (~23,5°C) y la presencia de girosciclónicos cerca de la costa. Esto coincidió con la riqueza mayor (de 5 a 9 especies dependiendo la escala espacial) de mamíferosmarinos en la zona. La especie dominante fue Megaptera novaeangliae (0,092 avistamientos km-1), la cual se distribuyó haciazonas costeras en aguas someras. Durante verano-otoño se registraron valores bajos de salinidad (32,8) y Chl-a (0,1 mg m-3). Sedetectó una disponibilidad alta de fosfatos (2,5 µM), la presencia de giros anticiclónicos y temperaturas altas (~31°C), coincidiendocon la riqueza más baja (3 especies) de mamíferos marinos. Stenella attenuata fue la especie dominante (0,036 avistamientoskm-1), cuyos individuos fueron encontrados distribuidos cerca de las costas de Jalisco y Colima (0-3mn), en aguas someras conuna disponibilidad alta de nutrientes inorgánicos. El análisis de componentes principales mostró que la batimetría (99.6%) fueel principal parámetro que explica la varianza de los datos, por lo que podría potencialmente modular aspectos ecológicos de losmamíferos marinos.

Palabras clave: Estructuras dinámicas de mesoescala, clorofila-a, temperatura superficial del mar, batimetría, mamíferos marinos

Abstract.- The oceanographic conditions that could influence richness and distribution of marine mammal species in the coastalarea of the Mexican Central Pacific (MCP) were investigated throughout 2011. Marine mammals observations were obtained fromtwo research platforms. CTD casts were deployed down to 100 m, water samples were taken monthly at six stations for determinationof organic nutrients, and another 15 stations were sampled over a wider area only during the winter. Satellite images from MODIS-AQUA L2 were used to obtain sea surface temperature (SST) and chlorophyll-a (Chl-a) values, likewise altimetry data to identifymesoscale dynamic structures in the region. High salinity values (34.6), low concentrations of nitrates and nitrites (~3-4 µM),silicates (5-7 µM), Chl-a (~10 mg m-3), and low SST (~23.5°C) were detected, as well as the presence of cyclonic gyres near the coastduring the winter-spring period. This coincided with high marine mammal species richness in the area (from 5 to 9 speciesdepending on spatial scale). The dominant species was Megaptera novaeangliae (0.092 sightings km-1), which was distributedclose to the coast in shallow waters. Low salinity (32.8) and Chl-a values (0.1 mg m-3) were detected during the summer-fall period.High phosphate availability (2.5 µM), presence of anticyclonic gyres, and high SST (~31°C) were also found, coinciding with lowspecies richness (3 species). The dominant species was Stenella attenuata (0.036 sightings km-1); those individuals were founddistributed near the Jalisco-Colima coast (0-3 nm) in shallow waters with high inorganic nutrient availability. The principalcomponents analysis showed that bathymetry (99.6%) was the main parameter explaining data variance; this parameter couldtherefore potentially modulate ecological aspects of marine mammals.

Key words: Mesoscale dynamic structures, chlorophyll-a, sea surface temperature, bathymetry, marine mammals

480 Kono-Martínez et al.Oceanography and marine mammals in the Mexican Central Pacific

INTRODUCTION

Marine mammals are considered protected species undernational and international agreements (e.g., Mexican Norm059-SEMARNAT-20101 and IUCN red list2). They are pelagicanimals with biological (breeding and feeding) and ecological(dispersion, distribution, migration, etc.) activities influenced byabiotic factors (Ballance et al. 2006, Laptikhovsky 2009,Rennie et al. 2009) such as the bathymetry, distance to thecoast, thermocline depth, temperature, water clarity, primaryproductivity (chlorophyll-a), and food availability (Bräger etal. 2003, Hastie et al. 2003, Danil & Chivers 2006, Rasmussenet al. 2011). Physical water properties are modulated by severaldynamic structures such as gyres (cyclonic and anticyclonic),upwellings, meanders, and filaments, among other systems thatare called mesoscale dynamic structures (MDS), based on theirsize (1-100 km) (Talley et al. 2011). The intensity of MDS inthe ocean depends in general on the gravity, density gradients,and wind effort, which produce the re-suspension or sinking ofparticles and organisms (Linacre et al. 2010). This allows theestablishment of complex trophic webs that generate availabilityof potential prey (Torres-Orozco et al. 2005), leading to theaggregation of top predators such as marine mammals (Rennieet al. 2009).

Fourteen species of marine mammals have been reported(Ortega-Ortiz et al. 2013) in the coastal region of the MexicanCentral Pacific (MCP), with high sighting rates of humpbackwhales (Megaptera novaeangliae) during winter, and ofspotted dolphins (Stenella attenuata) throughout the year(Ortega-Ortiz et al. 2011). However, few studies havedescribed the interaction between marine mammals and theirenvironment in coastal and tropical areas such as the MCPregion, where oceanographic parameters vary seasonally dueto anthropogenic and continental influences as well as to thepresence of storms (Salas et al. 2006). This particular zone islocated within a dynamic transition zone that generates variabilityin physico-chemical parameters and the increase of the region sprimary productivity (Galicia-Pérez et al. 2006, Kessler 2006,López-Sandoval et al. 2009).

Studies of the interaction between marine mammals andoceanographic parameters of the water column have suggestedthat MDS are the main factors influencing the presence ofcetaceans in northwestern Mexico (La Paz Bay, B.C.S.), wherewater column mixing and the increase in chlorophyll-a (Chl-a)concentrations favor the aggregation of potential cetacean prey

(Salvadeo et al. 2009, Pardo et al. 2013). Given thesecharacteristics and the fact that marine mammals are considered‘bio-indicators’ because they are sensitive to environmentalchanges that modify their habitats and/or the distribution/abundance of their potential prey (Moore 2008). Thus, wehypothesize that the typical variability of oceanographicconditions in the tropical region could influence the occurrenceand distribution of marine mammal species, reflecting theenvironmental quality. The aim of this study was therefore toidentify a potential relationship between the oceanographicconditions and the richness and distribution of marine mammalspecies in the coastal area of the MCP during 2011.

MATERIALS AND METHODS

STUDY AREA

This study was conducted mainly in the coastal area of Jaliscoand Colima, Mexico (between 19°35’ and 18°00’N, and103°30’ and 105°25’W), where the continental shelf (200 misobaths) extends ~13 km from the coast (Fig. 1). The area isinfluenced by the California Current (CC) flowing southwardsduring the winter-spring period, and by the Mexican CoastalCurrent (MCC) flowing northwards during the summer-fallperiod, with the highest intensity during the fall season (Wyrtki1967, Kessler 2006, Lavín et al. 2006a, Pantoja et al. 2012).Some authors have concluded that the topography andphysiographic traits of the coastline promote the formation ofMDS over the continental shelf in this region (Galicia-Pérez etal. 2006, Salas et al. 2006).

OCEANOGRAPHIC PARAMETERS COLLECTION

Due to the different effort in the surveys, we separated in twosampling categories: coastal surveys and a mesoscale survey,which covered a wider area.

COASTAL SURVEYS

Monthly samples were obtained at six stations located off thesouthern Jalisco and Colima coast during the periods of January-February and April-December 2011 from a 26 feet longoutboard motor vessel. Three stations were located 1.8 km (1nm) from the coast (coastal transect), and the other three werelocated 9.3 km (5 nm) from the coast (oceanic transect) (Fig.1).

1NORMA Oficial Mexicana NOM-059-SEMARNAT-2010. Protección ambiental-Especies nativas de México de flora y fauna silvestres-Categorías de riesgo y especificaciones para su inclusión, exclusión o cambio. Lista de especies en riesgo. <http://www.profepa.gob.mx/innovaportal/file/435/1/NOM_059_SEMARNAT_2010.pdf>2IUCN Global Species Programmed Red List Unit. The IUCN Red List of Threatened Species. IUCN, Cambridge. <http://www.iucnredlist.org/>


MESOSCALE SURVEY

In order to corroborate a potential pattern in distribution-richnessof marine mammals related with oceanographic parameters,during winter (at March), the expected period with a majorrate of sighting of marine mammals (Ortega-Ortiz et al. 2013),a survey in a wider area was conducted using a 42 feet longvessel. Five transects were established parallel to the coast,each one comprising three stations located 5.5 km (3 nm,coastal), 28 km (15 nm, intermediate), and 56 km (30 nm,oceanic) from the coast (Fig. 1).

Oceanographic parameters that describe productivity/stabilityconditions through the water column, such as temperature,salinity, mixed layer depth, nutrients, and chlorophyll-a, weredetermined during coastal as well as mesoscale survey. CTD(Sontek CastAway) profiles were constructed down to a 100m depth at the 21 sampling stations (coastal surveys andmesoscale survey). Water samples (100 ml) were taken at 0,25, and 50 m depths using 5L Niskin bottles. These sampleswere frozen until later analysis of inorganic nutrient concentration(nitrates and nitrites, phosphates, and silicates); these analyseswere carried out using a continuous flow auto-analyzer (Skalar

San Plus), following methods proposed by Grasshoff et al.(1983). The mixed layer depth was calculated following methodsproposed by Kara et al. (2000).

In addition, to describe oceanographic conditions in a widerscale for MCP region, level 2 images (~1 km and 1 day spatial/time resolution) of sea surface temperature (SST) and Chl-awere obtained from the MODIS Aqua sensor (NationalAeronautics and Space Administration)3. Monthly images with>70% coverage of SST and Chl-a concentration were laterextracted to identify mesoscale dynamic structures in the MCPregion. Altimetry data from the AVISO (Aviso User Service,France)4 program were also processed to identify circulationpatterns (with 1/3° resolution) in the area to analyze the satellitedata in integrated plots using ®MATLAB ver. 7.11 software(The MathWorks, Inc.). It was additional information to use asreference by integrating with the coastal information. Thestatistical analysis was also performed using ®MATLAB ver.7.11 software. Data did not have a normal distribution, and thenon-parametric tests Kruskal-Wallis (H) and Dunn (Q) weretherefore used with a 0.05 significance level.

Figure 1. Location of the sampling stations within the Mexican Central Pacific. Stations sampled during surveys conducted from a small boatoff the Jalisco-Colima coast (left). Stations sampled during the mesoescale survey during March 2011 (right) / Posición de las estaciones demuestreo en el Pacífico central mexicano. Estaciones muestreadas durante los cruceros realizados en embarcación pequeña en la costade Jalisco-Colima (izquierda). Estaciones muestreadas durante el crucero de mesoescala durante marzo 2011 (derecha)

3NASA, Gene C. Feldman.<https://oceancolor.gsfc.nasa.gov/data/aqua/>4<http://www.aviso.altimetry.fr/en/data.html>


MARINE MAMMAL SIGHTINGS

A path was surveyed between sampling stations during thecoastal and mesoscale surveys to record marine mammalsightings, at a speed between 7 and 9 knots. Sightings weredetected by three observers (at the bow, port, and starboard)using Fujinon® 7x50 binoculars. The geographical position,species, and number of animals of each sighting were recorded.The unit effort was estimated as the total distance travelled (km)during which marine mammals were searched for. Marinemammal sightings were standardized by calculating the sightingrate (SR) with the following equation:

SR = n / e

where n is the number of sightings and e is the effort in kilometers(Kiszka et al. 2007). The sighting rate during coastal surveyswas calculated for a) each season (winter: from January toFebruary, spring: from April to June, summer: from July toSeptember, and fall: from October to December), and for b)each month during 2011. The sighting rate during the mesoscalesurvey was additional information to integrate with the coastalinformation to carry out an exhaustive discussion about ourresults.

RELATIONSHIP BETWEEN OCEANOGRAPHIC PARAMETERS

AND DISTRIBUTION-RICHNESS OF MARINE MAMMALS

In order to identify a potential relationship between marinemammals and oceanographic data a principal componentsanalysis (PCA) was used, following the method proposed byClarke & Warwick (2001). The marine mammal data used forthese analyses were only the most frequently recorded speciesin the region (Ortega-Ortiz et al. 2011, 2013).

RESULTS

SEA SURFACE TEMPERATURE AND SALINITY DURING

COASTAL SURVEYS

Sea surface temperature (SST) varied significantly betweenseasons (H66,3= 37.83, P < 0.001). Minimum values (23.5ºC)were recorded during the winter-spring period, and maximumvalues (31.1ºC) were recorded during the summer season, withtemperatures decreasing (23.9ºC) in the middle of the fall season(Table 1). Spatial variation of temperature, at the surface aswell as at 50 m depth, was minimal (~1ºC) during winter-spring(H30,5= 0.95, P > 0.001); but warmer temperatures (27.5°C)were recorded at the surface at the southern oceanic station(Table 2). Spatial variation of temperature was also minimal(H36,5= 0.62, P > 0.001) during the summer-fall period, with amaximum value (29.2°C) at the surface at the intermediateoceanic station (Table 2).

Salinity varied significantly between seasons (H66,3= 25.58,P < 0.001), and had opposite patterns to Temperature: withmaximum values of 34.6 occurring during the winter-springperiod, and decreasing to minimum values of 32.8 during thesummer-fall period (Table 1). Spatial variation of salinity waslow (0.3) (H66,5= 0.84, P > 0.001) during the winter-springand summer-fall periods (0.5). The lowest salinity (33.4) wasrecorded at the surface at the coastal southern station, whereasthe highest salinity (33.9) was recorded at the surface at theoceanic northern station (Table 2).

Table 1. Seasonal variability of oceanographic parameters and mixed layer depth obtained from coastal surveys in the MexicanCentral Pacific during 2011. Mean and Rank values for temperature are included / Variación estacional de parámetros oceanográficosy capa de mezcla obtenidos de los cruceros costeros en el Pacífico central mexicano durante el 2011. Se incluyen valores mediosy rango de la temperatura


NUTRIENTS DURING COASTAL SURVEYS

Low concentrations of nitrates and nitrites (range: from 3.1 to4.7 µM), phosphates (range: from 0.7 to 1.4 µM), and silicates(range: from 5.2 to 7.4 µM) (Table 1) were recorded duringthe winter-spring period. Nutrient concentrations were higherduring the summer-fall period (range: from 3.6 to 8.4 µM);phosphate concentrations ranged between 0.6 and 2.5 µM, andsilicate concentrations ranged between 4.6 and 8.2 µM (Table1).

The spatial variation of nutrients was not statistically significant(H30,5= 3.49, P > 0.001) during winter-spring; however,maximum values of nitrate and nitrite (12.5-12.6 µM) weremeasured at the northern and southern oceanic stations. Therewas no spatial variability in the phosphate and silicateconcentrations during this period; values were similar betweenstations and depths (Table 2).

There was no spatial variability (H36,5= 1.19, P > 0.001)during the summer-fall period; however, high concentrations ofmainly nitrates, nitrites, and phosphates were recorded at thecoastal northern station at almost all sampled depths (Table 2).

MIXED LAYER DURING COASTAL SURVEYS

The water column was stratified with a well-defined mixed layer(ML) in the upper 10 m during winter and at the beginning ofthe spring season. The ML deepened to 20 and 23 m aroundthe middle of the spring season (Table 1). The ML deepened to18 m at the beginning of the summer season, then deepenedfurther to 32 m at the middle of the season, and shoaled to 22m at the end of this same season. The ML was thinner during

the fall season, decreasing at a depth of 10 m; by the end of thefall season the ML was situated at 13 m depth, and the watercolumn was again stratified (Table 1).

OCEANOGRAPHIC PARAMETERS DURING THE MESOSCALE

SURVEY

The sea surface temperature did not vary significantly betweenthe coastal (range: 25.4-27.5°C), intermediate (range: 23.6-27.8°C), and oceanic stations (range: 24.8-26.6°C) during themesoscale survey; this pattern was similar at 25 and 50 m depth.Salinity values were similar at all stations, and nutrients did notshow spatial differences, only silicates had higher values (28-33.1 µM) at the coastal stations, mainly at 25 m depth (33.1µM) (Table 3). The water column was stratified and with a well-defined mixed layer (ML) in the upper 15 m.

SEA SURFACE TEMPERATURE, CHLOROPHYLL-A, AND

ALTIMETRY IN THE STUDY AREA

A SST of 22ºC and Chl-a concentrations of 10 mg m-3 wererecorded near the coast during the winter-spring period in thenorthern part of the study area (Figs. 2 and 4). Similar valueswere also recorded in the oceanic zone, where a cyclonic gyrewas observed (Fig. 2a). By the middle of the winter-springperiod the circulation pattern changed from south to north, warmwaters were recorded (31ºC) (Fig. 2e), and the Chl-aconcentration decreased to 1 mg m-3 (Fig. 4e).

During the summer-fall period the circulation patternconsisted in water flow towards the northwest, with temperaturesof 31ºC and a minimal Chl-a concentration of ~0.1 mg m-3

Table 2. Spatial variability of oceanographic parameters obtained from coastal surveys in the Mexican Central Pacific during the cold (winter-spring)and warm periods (summer-fall) of 2011. Mean and rank values for temperature are included. Coast= coastal station. Ocean= oceanic station.1= Southern station. 2= Intermediate station. 3= Northern station (Left map from Fig. 1) / Variación estacional de parámetros oceanográficosobtenidos de los cruceros costeros en el Pacífico central mexicano durante los periodos frío (invierno-primavera) y cálido (verano-otoño) de 2011.Se incluyen valores medios y rango de la temperatura. Coast= estaciones costeras. Ocean= estaciones oceánicas. 1= estaciones del sur.2= estaciones intermedias. 3= estaciones del norte (mapa a la izquierda de la Fig. 1)


Table 3. Spatial variability of oceanographic parameters obtained from the mesoscale survey (March 2011) in the Mexican Central Pacific. Number1 refer the station in the most southern position and 5 is for the station in the most northern position (right map from Fig. 1) / Variaciónestacional de parámetros oceanográficos obtenidos en el crucero de mesoescala (marzo 2011) en el Pacífico central mexicano. El número 1 serefiere a la estación en la posición más sureña y el 5 para la estación en la posición más norteña (mapa a la derecha de la Fig. 1)

Figure 2. Sea surface temperature recorded by MODIS-Aquaoff the Mexican Central Pacific coast during: (a) January, (b)February, (c) March, (d) April, (e) May and (f) June 2011. Thearrows indicate the pattern of oceanic geostrophic currents,and the circles show cyclonic/anticyclonic gyres (white pixelsdenote unavailable data due to cloud cover) / Temperaturasuperficial del mar obtenida de MODIS-Aqua en la costa delPacífico central mexicano durante: (a) enero, (b) febrero, (c)marzo, (d) abril, (e) mayo y (f) junio 2011. Las flechas indicanel patrón de las corrientes geostróficas, los círculos muestranlos giros ciclónicos/anticiclónicos (pixeles en blanco denotanindisponibilidad de datos debido a cobertura de nubes)


Figure 3. Sea surface temperature recorded by MODIS-Aqua off the Mexican Central Pacific coast during: (a)July, (b) August, (c) September, (d) October, (e)November and (f) December 2011. The arrows indicatethe pattern of oceanic geostrophic currents, and thecircles show cyclonic/anticyclonic gyres (white pixelsdenote unavailable data due to cloud cover) /Temperatura superficial del mar obtenida de MODIS-Aqua en la costa del Pacífico central mexicanodurante: (a) julio, (b) agosto, (c) septiembre, (d)octubre, (e) noviembre y (f) diciembre 2011. Las flechasindican el patrón de las corrientes geostróficas, loscírculos muestran los giros ciclónicos/anticiclónicos(pixeles en blanco denotan indisponibilidad de datosdebido a cobertura de nubes)

over the entire area. Anticyclonic gyres were also observedmoving towards the northwest (Figs. 3a and 5a). By the middleof the summer-fall period the geostrophic circulation changedtowards the southeast; however, flow direction in the oceaniczone was towards the northwest (Figs. 3b and 5b). The SSToscillated between 30 and 31ºC, and there were Chl-aconcentrations of ~3 mg m-3 near the coast (Fig. 5c). Towardsthe end of this period there was a cold water intrusion (24ºC)at the northern area, and the circulation pattern consisted in asoutheast flow. There were Chl-a concentrations of ~0.1 mgm-3 near the coast (Figs. 3f and 5f).

MARINE MAMMAL SPECIES RICHNESS AND DISTRIBUTION

Seven marine mammal species were recorded in 188 sightingsduring coastal surveys. Only four species in 110 sightingsoccurred during winter season, for a sighting rate of 0.106sightings km-1. This rate was significantly different from thatobtained during the other seasons (spring: Q11,3= 2.58, summer:Q11,3= 1.92, fall: Q11,3= 0.93; P < 0.05). The species recordedduring winter coastal surveys were: Megaptera novaeangliae,Stenella attenuata, Steno bredanensis, and Stenellalongirostris (Table 4). The first two species were distributedmainly along the continental shelf edge, and within the bays ofManzanillo (Fig. 6).


A total of 14 sightings corresponding to five species wererecorded in the spring season, with a sighting rate of 0.025sightings km-1 (Table 4). The following species were identified:M. novaeangliae, S. attenuata, S. longirostris, Balaenopteraedeni, and T. truncatus. Individuals for first 4 species weresighted mainly near the coast, whereas T. truncatus individualswere sighted within Tenacatita Bay in Jalisco (Fig. 6).Balaenoptera edeni was observed only once and therefore itwas not possible to calculate a sighting rate (Table 4).

Three species in 19 sightings were recorded during thesummer, with a rate of 0.025 sightings km-1 (Table 4). Stenella

attenuata and S. bredanensis were sighted at the continentalshelf limit near the coast, whereas T. truncatus was sightedonly in the same bay of Jalisco.

A total of 45 sightings corresponding to 5 species wererecorded during the fall, with a rate of 0.047 sightingskm-1 (Table 4). The following species were recorded: S.attenuata, S. bredanensis, T. truncatus, M. novaeangliae,and Z. californianus; this last species was observed only onceand therefore it was not possible to calculate a sighting rate. Allspecies were sighted near the coast of Colima, and only T.truncatus was sighted inside Tenacatita Bay (Fig. 6).

Figure 4. Chlorophyll-a concentration recorded byMODIS-Aqua off the Mexican Central Pacific coastduring (a) January, (b) February, (c) March, (d) April,(e) May and (f) June 2011. The arrows indicate thepattern of oceanic geostrophic currents, and the circlesshow cyclonic/anticyclonic gyres (white pixels denoteunavailable data due to cloud cover) / Concentraciónde Clorofila-a obtenida de MODIS-Aqua en la costa delPacífico central mexicano durante: (a) enero, (b)febrero, (c) marzo, (d) abril, (e) mayo y (f) junio 2011.Las flechas indican el patrón de las corrientesgeostróficas, los círculos muestran los giros ciclónicos/anticiclónicos (pixeles en blanco denotan indisponibilidadde datos debido a cobertura de nubes)


Furthermore, nine marine mammal species were recordedduring the moesoscale survey conducted in March 2011,including the seven species recorded during coastal surveys aswell as Grampus griseus and Kogia spp. Only onceBalaenoptera edeni was observed, and a sighting rate wastherefore not calculated for this species. The most sighted specieswere M. novaeangliae (0.012 sightings km-1) and S. attenuata(0.003 sightings km-1) (Table 5). Most M. novaeangliae andS. attenuata sightings occurred near the coast, where SST

values were higher than 27°C. Grampus griseus and Kogiaspp. individuals were sighted at the continental shelf edge, whereSST was decreasing (26°C); whereas S. longirostris, S.bredanensis, and Z. californianus individuals were sightedtowards the north near the coast in front of a cold current (24°C)flowing perpendicular to the mainland. Finally, T. truncatusindividuals were sighted within Tenacatita Bay (Fig. 7).

Figure 5. Chlorophyll-a concentration recordedby MODIS-Aqua off the Mexican Central Pacificcoast during (a) July, (b) August, (c) September,(d) October, (e) November and (f) December2011. The arrows indicate the pattern of oceanicgeostrophic currents, and the circles showcyclonic/anticyclonic gyres (white pixels denoteunavailable data due to cloud cover) /Concentración de Clorofila-a obtenida deMODIS-Aqua en la costa del Pacífico centralmexicano durante: (a) julio, (b) agosto, (c)septiembre, (d) octubre, (e) noviembre y (f)diciembre 2011. Las flechas indican el patrónde las corrientes geostróficas, los círculosmuestran los giros ciclónicos/anticiclónicos(pixeles en blanco denotan indisponibilidad dedatos debido a cobertura de nubes)


RELATIONSHIP BETWEEN OCEANOGRAPHIC CONDITIONS

AND RICHNESS-DISTRIBUTION OF MARINE MAMMAL

SPECIES

The PCA analyses based on information from coastal surveysgenerated two principal components. The first was associatedwith the bathymetry, which explained 99.63% of total variance,and the second was associated with Chl-a concentration, whichexplained 0.20% of total variance (Fig. 8-left), suggesting thatthe first component was dominant. A similar result was obtainedwith the PCA based on information from the mesoscale survey.Two principal components were generated, one of which wasassociated with bathymetry, and explained 99.5% of the datavariance (Fig. 8-right).

Figure 6. Location of the most frequent marine mammal species into the coastal zone of Mexican Central Pacific during winter-spring(left) and summer-fall (right). Black triangle: Megaptera novaeangliae. White diamond: Stenella attenuata. Black square: Tursiopstruncatus / Localización de las especies de mamíferos marinos más frecuentes en la zona costera del Pacífico central mexicanodurante invierno-primavera (izquierda) y verano-otoño (derecha). Triángulo negro: Megaptera novaeangliae. Diamante blanco:Stenella attenuata. Cuadrado negro: Tursiops truncatus

Table 4. Sighting rates (SR) of marine mammal species calculated based on surveys conducted from a small boat off the Jalisco-Colimacoast during 2011. Total search effort is also included / Rangos de avistamiento (SR) de especies de mamíferos marinos calculados enbase a los cruceros en las embarcaciones pequeñas en la costa de Jalisco-Colima durante el 2011. El esfuerzo total también esincluido

Table 5. Sighting rates (SR) of marine mammal species calculated basedon the mesoscale survey (March 2011) in the Mexican Central Pacificregion. Total search effort is also included / Rangos de avistamiento(SR) de especies de mamíferos marinos calculados en base al crucerode mesoescala (marzo 2011) en el Pacífico central mexicano. Elesfuerzo total también es incluido


Figure 8. Principal component analysis (PCA) of the oceanographic parameters and the dominant marine mammal species duringcoastal surveys (left) and the mesoscale survey (right). Crosses: Megaptera novaeangliae. Circles: Stenella attenuata / Análisis decomponentes principales (ACP) de los parámetros oceanográficos y las especies dominantes de mamíferos marinos durante loscruceros costeros (izquierda) y el crucero de mesoescala (derecha). Cruces: Megaptera novaeangliae y Círculos: Stenella attenuata

Figure 7. Sea surface temperature and marine mammal distribution observed during the mesoscale survey in March 2011.Other species (S. longirostris, Steno bredanensis, Grampus griseus, Kogia spp., Tursiops truncatus, Zalophus californianus) /Distribución de la temperatura superficial y de mamíferos marinos observada durante el crucero mesoescala en marzo2011. Otras especies (S. longirostris, Steno bredanensis, Grampus griseus, Kogia spp., Tursiops truncatus, Zalophus californianus)


DISCUSSION

Oceanographic conditions were similar during winter and spring,and during summer and fall 2011, so that two periods could bedefined in the MCP: cold (winter-spring) and warm (summer-fall). This oceanographic pattern has been previously describedby Filonov et al. (2000). Moreover, this pattern could describea relationship between habitat characteristics and the distributionof the most frequent (>30 sightings) cetacean species in theMCP region: M. novaeangliae and S. attenuata (Ortega-Ortizet al. 2011), which had been no described before.

OCEANOGRAPHIC CONDITIONS AND RICHNESS-DISTRIBUTION

OF MARINE MAMMAL SPECIES DURING THE COLD PERIOD

(WINTER-SPRING)The presence of the CC was observed during this period, withcold waters (<22ºC) flowing from the north. The influence ofthe CC has been reported in this area by several authors (Fiedler& Talley 2006, Lavín et al. 2006b, López-Sandoval et al.2009). The SST images and geostrophic currents indicatedseveral MDS, mainly cyclonic gyres (Figs. 2 and 4), which hadpreviously been reported as the main fertilizing processespropagating near the continental shelf (200 m) in this region ofthe MCP (Salas et al. 2006, Pantoja et al. 2012). The MDScould have resulted in the lifting/sinking (~20 m) of isotherms,allowing cold-water intrusion towards the surface, as has beendescribed by some authors (e.g., Torres-Orozco et al. 2005,Salas et al. 2006, López-Sandoval et al. 2009). Althoughgyres could not be clearly identified by AVISO data within thestudy area (due to the 1/3° data resolution); however, the SSTand Chl-a satellite data were useful to identified some of thesestructures that have been described during the entire year. Theywere formed as the result of the interactions among continentalinputs, coastal circulation, and marine topography (Galicia-Pérezet al. 2006, Salas et al. 2006).

The MDS have been reported to affect characteristics ofthe water column such as mixed layer depth and inorganicnutrient distribution (Arístegui et al. 2003, Salas et al. 2006,Rennie et al. 2009). The main forcing agents that could generatevariations in the mixed layer depth are differences in windintensity, and differences in current intensity (such as the CCand MCC), as has been reported by Linacre et al. (2010).However, given that there are no data on wind intensity in thestudy area for 2011, we hypothesize that wind intensity wasprobably low, and therefore a mixed layer was formed at ~10mdepth.

Inorganic nutrient concentrations were high below the mixedlayer (25 and 50 m depth, Table 2), which could have resultedfrom transport (gyres and upwellings) towards the subsurface(Martin & Richards 2001), and from variations in nutrientconcentrations resulting from phytoplankton consumption(Falkowski 1997). The high Chl-a values recorded suggest afertilization event in the area, which could have been caused bythe shoaling of the thermocline associated with cyclonic gyres(Fig. 4). These results coincide with those reported by López-Sandoval et al. (2009), who characterized this period asproductive because that is when maximum values of primaryproductivity and Chl-a occur, and it is also when sunlight andoceanographic conditions are favorable for phytoplanktongrowth.

Another factor that could have influenced the presence ofcold waters in the northern part of the study region (Fig. 2a-d)is the occurrence of upwelling events such as those that havebeen reported near Cabo Corrientes during the winter-springperiod (Filonov et al. 2000, Torres-Orozco et al. 2005,Kessler 2006, López-Sandoval et al. 2009). The NOAAupwelling index5 for this period suggests an upwelling event,with cold water being transported by winds and marine currentsfrom the northwest, as has been described by Fiedler & Talley(2006). Additionally, the already-mentioned geostrophiccirculation pattern could have favored the formation of gyres inthe study area. These gyres could have had repercussions onnutrient and Chl-a concentrations, as was explained previously.This pattern was observed in the SST and Chl-a images, withconcentrations above 10 mg m-3 near the coast, coinciding withhigh nutrient values (>20 µM) (Figs. 2 and 4).

The species richness recorded during winter-spring periodin coastal surveys was relatively constant; however, a higherrichness was recorded during the mesoscale survey possiblybecause a wider region was surveyed and species with oceanichabits were also sighted (i.e., Kogia spp. and Grampusgriseus). Some of these species have also been associated withtemplate environments (i.e., Stenella longirostris, Kogia spp.and Zalophus californianus) due to the temperature effectson prey distribution (Davis et al. 2002), and therefore nosightings would be expected during other periods.

The sighting rate calculated based on coastal surveyscompared with the sighting rate obtained based on data fromthe mesoscale survey constitutes evidence that the coastal areais the most important habitat for the distribution of these species,mainly for M. novaeangliae, the most sighted species duringthe winter season (Table 4).

5<ftp://orpheus.pfeg.noaa.gov/outgoing/upwell/monthly/upindex.mon>


Studies on M. novaeangliae distribution report that thisspecies uses areas with similar characteristics to those of theMCP to carry out breeding and calving activities, because warmtemperatures (~28ºC) allow calves to thermoregulate, and thepresence of semi-enclosed coastal bodies and shallow depthsprovide calves with protection from predators (Calambokidiset al. 2001, Rasmussen et al. 2011).

The oceanographic conditions recorded during this studysuggest that several potential cetacean prey (zooplankton, fish,squid, among others) could have been transported to the area(Franco-Gordo et al. 2004, León-Chávez et al. 2010).Megaptera novaeangliae individuals could have been feedingopportunistically in the area, as has already been reported fornearby regions such as the Gulf of California (Gendron & Urbán1993) and the Oaxaca coast (Villegas-Zurita & Castillejos-Moguel 2013). However, the most commonly recordedbehavioral activities of this species in the region have beenassociated with breeding (García-Valencia 2016).

The second most frequently sighted species during the coldperiod was S. attenuata. This species was distributed near thecoast, which resulted in a high correlation between its densityand bathymetry. It has been reported that this species has anaffinity for tropical waters with a deep thermocline (~40 m)(Reilly 1990) and is distributed in areas with shallow depthsthat are used for resting, feeding, and finding refuge (Forcada2002), as was seen in the present study.

The sighting rates of other odontocete species were lower,indicating that their presence off the Jalisco and Colima coastcould be associated with ecological aspects similar to thoseaffecting S. attenuata. It is also possible that these species usethe region as a transit area on their way to other regions of thePacific Ocean with the exception of T. truncatus, which wereobserved in Tenacatita Bay, during all sampling period. Even,repeated observations on the same individuals suggesting thatthis could be a resident pod (Rossbach & Herzing 1999). Thisis a common characteristic for this species that had beenreported in other sites (e.g., Sellas et al. 2005, Galindo 2007,Vázquez-Castán et al. 2007, Martínez-Serrano et al. 2011).However, similar survey effort is needed during other periodsto explain the ecology of these species.

OCEANOGRAPHIC CONDITIONS AND DISTRIB UTION-RICHNESS OF MARINE MAMMAL SPECIES DURING THE WARM

PERIOD (SUMMER-FALL)The oceanographic conditions during this period could havebeen due to an increase in solar radiation and to the advectionof heat from the MCC in the equatorial region (Filonov et al.2000). This pattern is caused by a weakening of the

northwesterly winds; this allows the MCC to flow northwards,transporting warm waters (29-30ºC) from the North EquatorialCurrent (e.g., TPSW) (Wyrtki 1967) and unproductive watersfrom the Gulf of Tehuantepec (Gonzalez-Silvera et al. 2004,Fiedler & Talley 2006, Kessler 2006). The MCC created MDSwhich could be seen in the SST and Chl-a images (Figs. 2 and3), and influenced the availability of these parameters.

The temperature was homogeneous along the water columndue to the presence of anticyclonic gyres. These oceanographicsystems resulted in the sinking of isotherms, and in the mixing ofthe upper meters of the water column (Arístegui et al. 2003).The detection of gyres near the coast was difficult due to theresolution of geostrophic data (~20 km). On the other hand,the presence of internal waves, which have been reported inthis area (Filonov et al. 2000) near the continental shelf, couldhave resulted in the sinking of isotherms and could havecontributed in this way to a non-stratified water column nearthe coast. The low salinity values recorded in the study areaduring the warm period are related to continental discharge fromthe coastal zone (Olivos-Ortiz et al. 2008). The rainy seasonoccurs between June and October; this is the period whentropical storms pass through the area (Servicio MeteorológicoNacional, México)6.

The variations in nutrient and Chl-a concentrations duringthis period could have been influenced by the already-mentionedtemperature increase (up to 30ºC at the surface) associatedwith the transport of less productive waters. Temperature is anabiotic factor that is crucial for phytoplankton growth andnutrient assimilation. Values above 28ºC inhibit phytoplanktongrowth (Rhee & Gothan 1981, Neori & Holm-Hansen 1982).This suggests that low Chl-a concentrations were due to lowprimary productivity caused by the temperature increase, whichcoincides with what was reported by López-Sandoval et al.(2009), who found low primary productivity associated withwarm tropical waters such as the TPSW during this period.Nutrient concentrations, mainly of phosphates, were high (>2µM) during the middle of the warm period (Table 1). This waslinked to the beginning of the rainy season, when continentalinputs contain higher nutrient concentrations, and partly to thevertical flow from the bottom to the subsurface due to thepassage of storms and hurricanes (such as ‘Jova’, Lujano-Bravo& Hernández-Unzón 2011). These meteorological events havebeen identified as mechanisms that cause ascending flow in thewater column, resulting in temporal upwelling (Davis & Yan2004, Walker et al. 2005).

6<http://smn.cna.gob.mx/>


The lowest marine mammal species richness was recordedduring summer; however, an increase in species richnessoccurred during fall, which suggests that conditions were similarto winter conditions. The sighting rate increased to 0.047sightings km-1, mainly of S. attenuata, coinciding with the laterperiod of higher temperatures and deeper thermocline (~30 m),which are optimal conditions for feeding activities. Stenellaattenuata feeds on a wide variety of fish (27 families), oncephalopods (17 families), and on some decapods (Galatheidae)(Perrin 2002). Some pelagic and reef fish species also spawnduring this period (Silva-Segundo et al. 2006). These could bepotential prey and the area could serve as a feeding area (May-Collado & Forcada 2012). It has been reported that theabundance of S. attenuata increased during the period of lowwater levels at the end of the rainy season in Costa Rica in theGulf of Papagayo, when coastal upwellings also occurred,because abundance decreased significantly during the remainderof the year (May-Collado & Forcada 2012). This pattern couldbe similar to what has already been described about intermittentupwellings in our study area.

Megaptera novaeangliae individuals were recorded at theend of this period, coinciding with the transition phase towardswinter. The recorded temperatures of 26-27ºC could havefavored their presence in this area to carry out reproductiveactivities during the next cold period (Calambokidis et al. 2001).In another hand, sightings of T. truncatus during this periodconfirmed its potential residence in Tenacatita Bay. Othercetacean species such as S. longirostris were not sighted duringthis warmer period, probably because their occurrence is relatedwith environmental changes from the region.

In summary, the dynamics of the MCP region createdfavorable oceanographic conditions that allowed the aggregationof marine mammals mainly during the cold period to conductfeeding activities (by dolphins), and breeding activities(particularly by M. novaeangliae). However, it is important tokeep in mind that the year 2011 was atypical because it wasinfluenced by the cold phase of ENSO (La Niña)7; and probablyour described relationship could be biased. Therefore, moreresearch must to be conducted during a year with typicaloceanographic conditions or over a longer period, tocorroborate if the depth of the study area is the only parameterthat determined species richness and distribution of marinemammals in the MCP region.

ACKOWLEDGMENTS

This bachelor research was possible by the Programa deMejoramiento al Profesorado PROMEP-SEP and ComisiónFederal de Electricidad for funding marine mammal surveys inthe region; the Facultad de Ciencias Marinas y CentroUniversitario de Investigaciones Oceanológicas of Universidadde Colima (U. de C.) for logistical support; the Secretaría deMedio Ambiente y Recursos Naturales through the DirecciónGeneral de Vida Silvestre Mexico for providing the SGPA/DGVS/00447/11 permit for field research. To the Mary ChuyIII crew and captains Oscar Enciso and Ivan Livas, besides thestudents of the Grupo Universitario de Investigación deMamíferos Marinos (GUIMM) of the U. de C. and volunteersfor the support in the field.

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Received 4 June 2016 and accepted 24 July 2017

Editor: Claudia Bustos D.

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